Battery voltage protection relay - anyone used one?

[garethj]

Hello, experts.

 

Mrs_garethj's 2003 Jaguar S Type sometimes runs down its battery overnight.  I very kindly gave the local independent Jaguar garage £750 to fix it, then another £500 when that didn't work, and the problem is exactly the same, except I'm now £1250 worse off.

 

I could give him more money to have another go, but as I'm not the Sheikh of Qatar I can't afford to keep handing money over to not resolve the problem.

 

It's our old friend the intermittent problem; sometimes the car is fine but occasionally the battery will be so flat the following morning that it won't even pop the central locking.  This makes diagnosis difficult, and disconnecting the battery every night is a bit of a faff, plus that throws up loads of error codes when driving.

 

Would something like this work?  It's for boats and motor homes where (I think I understand this correctly) it allows all the electrics to run until it gets to a pre-determined level, where it shuts everything off.  This means you can still start the engine in the morning if you've left some lights on overnight.

 

If I've got this right, it's a good solution.  It means the car can do its alarm stuff and module sequenced shutdown overnight, but if something fucks up as it sometimes does, we can flick a switch in the morning and the car will start.

 

Anyone used one before, or am I on the wrong track?

[spike60]

If it's completely discharging a large battery that's a lot of energy going somewhere, is the cut off man enough for that? I've had Bmw's do it with rear screen relays and heater resistor "hedgehogs", there aren't that many things can soak up that amount of energy without getting very hot. If it tries to power the rear screen or whatever through the small wire there may be trouble ahead if that's how it works.

[garethj]

That one says it'll cope with 200A.  I believe the car is waking up in the night for some reason, it's normal for it to pull 4A while it goes back to sleep again.  If it does that 8-10 times a night it's enough to take the battery down a lot.  And if it's doing it most nights, the poor old battery is getting more punishment than it can take.

[castros_bro]

I am not sure if it will do what you want.  As you crank the engine to start it the battery voltage drops due to the vast current draw.  If this voltage is below the "Brain" preset voltage then it will disconnect whilst you are trying to start, by disconnecting the battery the voltage will rise to above the "Brain" preset value and the battery will be reconnected. Could be interesting and unpleasent.

[dave21478]

Thats interesting. My Gaylander runs its battery down flat over the course of a couple of days if its not run.

Its drawing about 20 times more current at idle than others according to a quick poll on a landy forum, and despite pulling all the fuses one by one it still does it, so its not something fused, which means ECUs or alarm or something.

[garethj]

I am not sure if it will do what you want.  As you crank the engine to start it the battery voltage drops due to the vast current draw.  If this voltage is below the "Brain" preset voltage then it will disconnect whilst you are trying to start, by disconnecting the battery the voltage will rise to above the "Brain" preset value and the battery will be reconnected. Could be interesting and unpleasent.

You might be right.  Arse.

 

Thats interesting. My Gaylander runs its battery down flat over the course of a couple of days if its not run.

Its drawing about 20 times more current at idle than others according to a quick poll on a landy forum, and despite pulling all the fuses one by one it still does it, so its not something fused, which means ECUs or alarm or something.

I think my problem is similar.  Because the ECUs draw power from lots of different sources, pulling fuses doesn't work like in the olden days

[Parky]

As a short term solution, can you not just disconnect the battery each night or will that set off alarms and upset ECU's on the S type?

 

I had a similar problem with an old Vauxhall (orl vocksorls ar shit) which admittedly was Luddite technology and the battery disconnect was the only way I could guarantee getting to work each day. Turned out the earth lead from engine to chassis was loose which I discovered after experts including Hometune, Vauxhall, and the AA diagnosed as failed battery, failed alternator, and failed starter. Half a turn on a 13mm bolt solved the problem. I was well pissed off about that.

[Mr_Bo11ox]

Argh, 1250 to not fix a problem, I'm not sure that I could continue living after that

[Stixy]

Why do modern motors need to do things while they should be switched off   ?

 

My wife had a 2008 Mondeo  and one night about 11.30 ish i was on my laptop in the sitting room  missus had gone to bed and car was outside  supposed to be "off"  and i had a message pop up on my screen saying  " Ford audio wants to connect  Y or N ? "    ( bluetooth )

 

Why ? 

[garethj]

As a short term solution, can you not just disconnect the battery each night or will that set off alarms and upset ECU's on the S type?

You can, but it does strange things to the ECU and the next drive has most of the warning lights on, including a few worrying ones about brakes.

 

Argh, 1250 to not fix a problem, I'm not sure that I could continue living after that

"Hello, Autoshite Samaritans, can I help you find some rope?"

 

I had planned to spend that on something unsuitable from ebay to offset the dullness of my Skoda.  Instead I gave it to a garage.  While it's an unpleasant thought, the worse one that's keeping me awake at night is what to do next.

 

Take it to the same place, where they've proved they can't find the problem?  Take it somewhere else, where the first thing they'll say is "I wouldn't have done it like that, of course we'll have to replace those bits again to make sure it's done properly."  Take it to a main dealer, where they might be able to fix it for £1200 a day?

 

I don't like any of those.

[Mr_Bo11ox]

Me neither. I dont know what the answer is

[jonathan_dyane]

Sell it.

[robinmasters]

Disconnect battery. Advertise. Reconnect battery just before buyer arrives. Sell it. Throw pay as you go mobile in canal.

EFA

[overrun]

Why do modern motors need to do things while they should be switched off   ?

 

My wife had a 2008 Mondeo  and one night about 11.30 ish i was on my laptop in the sitting room  missus had gone to bed and car was outside  supposed to be "off"  and i had a message pop up on my screen saying  " Ford audio wants to connect  Y or N ? "    ( bluetooth )

 

Why ?

 

The real question here is why did you have your bluetooth still turned on?

[Stixy]

The real question here is why did you have your bluetooth still turned on?

 

Diddnt even know it was on  , also im not really sure what it does ?

[twosmoke300]

Take it back to the dealer and demand it's fixed foc as you have already paid 1200 for them to do that . Piss poor diagnosis.

[Micrashed]

Take it back to the dealer and demand it's fixed foc as you have already paid 1200 for them to do that . Piss poor diagnosis.

THIS is what I would be doing.

 

If that didnt work I may* (in this order)

 

• Write to the SMMT if they are a member and ask for their input
• Speak to trading standards
• Speak to the LOCAL press who love a good* story of punters being hard done by and ripped off.
• Park the car outside the dealership on the road with a list of the problems placed inside the window and what the dealer has failed to do.
• Take the dealership manager on a test drive to demonstrate the problem and then abandon him several miles from the dealership down a country lane in pre mobile phone days.

Worked for me anyway.

[garethj]

Yes, I agree with that, it's absolutely perfect.  But I don't think it'll work.

 

When I took the car there, I asked for them to fix the problem.  I didn't write this down.  On the receipt, the work is listed with replacement parts so if things got arsey they can just claim I asked for them to replace these things.  I'm not saying they would, but legally I'm on shaky ground.

 

This kind of fault could be a sticky central locking solenoid which is just on the point of telling the car it's being unlocked.  Or a module somewhere.  Or some wire that's got wet and is high resistance.  Or a connector that's got some corrosion.  That's a lot of things to check through at £50 an hour, plus parts.

 

If I took the car in with a flat tyre and they replaced the passenger's seat, I'd have some justification, but I don't think it's as straightforward as that.

 

But I'll phone up the people selling that battery isolator on Tuesday and ask them if it works as I'm hoping.

[spike60]

Has the car been to a Jag or diagnostics specialist? A regular garage will have a scanner that does most things on most cars but to read the full data on a complex car more specialist gear is needed. When I had Merc alarm troubles a £3k Snap On scanner was no help, an £11k(!) Bosch scanner identified the trigger.

[garethj]

Yes, it's at an independent Jaguar specialist.  Probably better than a main dealer because they see a lot more 10 year old Jags than a main dealer does.

 

Perhaps I need to invent a tester that connects to the wiring loom and checks for high resistance.  I think all the existing diagnostics check for modules and for their readings they assume the wiring is ok.

[Des]

I had a similar problem, it was the radiator fan relay all damp and corroded internally, I wonder if changing all your fuses for the weakest available of an evening, and then seeing if any have blown in the morning would point to which circuit is at fault, if it's one of the many non essentials, as in everything bar ignition and horn, leave the fuse/s out.

[garethj]

I don't think that would help either, unfortunately.  It's fine that the system is working, it's not fine that it's working several times a night.

[Joey spud]

British Gas have very similar battery savers fitted to their Transits and Caddys and they work really well.

 

They are fitted into the main live lead and if the battery level drops below a set level the relay opens and cuts all power to the van,you then just press the yellow reset button and in theory there is still enough charge available to restart,although you will still need to reset/code stuff as req.

 

I guess B.G must of had a lot of engineers calling in on a monday morning or after being on leave with dead vans to deem it necessary to fit them.

[Inspector Morose]

A good few bus companies use them as well. Far better at 3 in the morning to press the reset and start the bus than the engineer lugging the boost pack round to numerous dead buses to meet service.

 

Optare solos have a tendency to 'go to sleep' when the batteries go flat needing it to be re-booted by laptop so battery guards are a godsend for these.

[garethj]

Excellent, thanks chaps!

 

Selling the car isn't an option that Mrs_garethj wants to pursue

[PiperCub]

I'm sure you've tried this but if not, try:

Discon-ing the earth lead to battery

Put a multimeter switched to amps in series with (ie: between) discon'd lead and battery

Note reading (should be only a few milliamps) with everything switched off incl any interior lights

If the reading seems abnormally high, pull the fuses one by one and look for the reading to drop sharply - if this happens you've found your current drain that's flattening your battery.

 

This will at least identify the circuit that's the problem if not going as far as diagnosing the actual reason.

 

Agree with above - why do modern cars need to have stuff running when switched off aside from security measures.

[garethj]

Sadly that doesn't work on these multiplexed modern things. The ECUs get feeds from all kinds of places so the old fuse trick doesn't isolate it.

 

Also, it doesn't happen all the time, last night it was fine, but 2 nights ago it was draining the battery slowly.

[twosmoke300]

The way of testing for parasitic drain is still the same but you have to allow time for the can bus to power down and sleep . Normaly this is 2-3 minutes but some (esp bluetooth) can take up to 20mins to power down. It makes the task of finding a drainvery drawn out.

[garethj]

The Jaguar apparently draws 4 amps for a few minutes, then the current drops slowly and it doesn't go fully to sleep until 45 minutes later.  But because it doesn't wake up all the time, and I don't know how often, that makes fault finding almost impossible I reckon?

 

The hair brained scheme in my head is to put an amp clamp around the main battery lead, or even a voltmeter on the battery, then get an app on my phone which takes a photo every few minutes, while it's locked in the boot overnight.  Then I can look at the video in the morning and see what happens.  But then I do what - pull out a fuse every night until it doesn't draw any current?

 

If the fault only happens once a week and there are 80 fuses, the car will have fallen to pieces by the time I find the problem.

[twosmoke300]

any water leaks anywhere? have a look under all the carpets esp in the boot as iirc there is a fusebox under the boot floor on these